Metal ball bats are being used as substitutes for wooden bats because of their light weight. While all sorts of metals might be used, aluminum and its alloys are especially well suited for the purpose, considering strength, weight ratio, surface characteristics, formability, corrosion resistance and cost. While aluminum bats presently cost more than wooden bats, they have the great advantage of lasting longer, and hence of costing less in the long run.
Early efforts to develop aluminum bats included the approach of swaging down a length of a cylindrical extrusion or tube. The extrusion is swaged down by striking or contacting the member with clapping hammers which repetitively strike the outer surface of the extrusion. The striking motion is perpendicular to the longitudinal axis of the tube which causes the exterior diameter of the tube to be reduced thus forming an intermediate tapered portion (also referred to as the trumpet) and handle end of the ball bat.
A bat made in this way has a generally smooth outer surface. However, the interior surface of a ball bat formed by conventional methods is less than smooth. It may have cracks or fractures which run parallel to the longitudinal axis of the ball bat. The cracks weaken the bat and reduce its longevity and are sites for the propagation of stress corrosion cracking.
The swaging process does not result in a uniform wall thickness of the trumpet section. If a prescribed minimum wall thickness is to be achieved, portions of the trumpet will have a wall thickness which greatly exceeds the minimum. The increased wall thickness adds to the weight of the bat. This weight does not contribute to the strength of the bat, and it displaces the center of gravity of the bat away from the hitting end of the bat. In addition, folds of metal form on the inner wall in the swaging process. These metal folds act as sites that initiate stress corrosion cracking. Furthermore, the metal folds add weight to the trumpet and handle of the ball bat.
Accordingly, it would be advantageous to provide a method of forming metal ball bats that results in a smooth crack-free interior surface.
The primary object of the invention is to provide a method of forming metal ball bats with a reduced wall diameter in the trumpet and handle end of the bat that meets the necessary strength requirements.
Another object of the present invention is to provide a method of forming metal ball bats with an increased uniformity in wall thickness in the trumpet and handle end of the bat.
Still another object of the invention is to provide a method of forming metal ball bats with a decreased level of cracks in interior surface of the trumpet and handle end of the bat.
These and other objects and advantages of the present invention will be more fully understood and appreciated with reference to the following description.